1. Field of the Invention
The present invention relates to a method of recovering a cleaning agent containing copper oxide as a component thereof, a cleaning agent containing basic copper carbonate as a component thereof, a cleaning agent containing copper hydroxide as a component thereof, or a cleaning agent containing copper oxide and manganese oxide as components thereof. More particularly, the invention relates to a method of recovering a copper component and/or a manganese component from a cleaning agent that has been used for removing a phosphine or a silane gas contained in a discharge gas from a semiconductor production step or a similar step.
2. Background Art
In the production steps for silicon semiconductors, compound semiconductors, etc., phosphines and hydrides (gaseous form) such as silane and disilane are employed as source gas or doping gas. Dichlorosilane is used as a source for forming silicon nitride (Si3N4) film on a semiconductor substrate such as a silicon wafer. These gases are highly harmful, and adversely affect the human body and environment if discharged to the atmosphere without any treatment. Therefore, the gases which contain these compounds and have been used in the semiconductor production steps must be cleaned prior to discharge to the atmosphere. In order to perform cleaning, there have conventionally been developed cleaning agents for harmful gases containing as a harmful component a phosphine, a silane, a disilane, or a dichlorosilane gas.
Regarding a method of cleaning a harmful gas containing a phosphine or a silane gas, the present applicant has developed a number of cleaning methods employing a cleaning agent containing copper oxide, or copper oxide and manganese oxide. According to one such cleaning method, a harmful gas containing a hydride gas such as phosphine is cleaned through contact with a cleaning agent formed of cupric oxide and an oxide of silicon and/or aluminum (Japanese Patent Application Laid-Open (kokai) No. 61-129026). Japanese Patent Application Laid-Open (kokai) Nos. 62-286521 to -286525 disclose methods of cleaning a similar harmful gas through contact with a cleaning agent formed of cupric oxide and an oxide of titanium, zirconium, lanthanum, iron, cobalt, nickel, tin, lead, antimony bismuth, vanadium, molybdenum, tungsten, niobium, or tantalum.
Japanese Patent Application Laid-Open (kokai) No. 1-254230 discloses a method of cleaning a harmful gas containing arsine, silane, etc. by bringing the gas into contact with a cleaning agent formed of a composition containing manganese dioxide, copper oxide, and cobalt oxide serving as predominant components and a silver compound. Japanese Patent Application Laid-Open (kokai) No. 6-154535 discloses a method of cleaning a similar gas through contact with a cleaning agent formed of a composition containing manganese dioxide and copper oxide serving as predominant components and a potassium component, onto which composition a silver compound is adsorbed.
Cleaning agents containing other copper compounds include a gas treatment agent for treating a discharge gas containing a Group V inorganic compound discharged from a production step for a Group III-V compound semiconductor thin film, which agent comprises a copper compound such as basic copper carbonate (disclosed in Japanese Patent Application Laid-Open (kokai) No. 8-59391); a gas treatment agent for treating a discharge gas containing a Group V organic compound and a Group V inorganic compound discharged from production step for a Group III-V compound semiconductor thin film, which agent is prepared by mixing basic copper carbonate and potassium permanganate with anatase titanium oxide microparticles (disclosed in Japanese Patent Application Laid-Open (kokai) No. 8-155258); and a solid removing agent for removing, in a dry process, harmful components contained in a discharge gas such as volatile inorganic hydrides and halides, which agent contains crystalline cupric hydroxide as a predominant reaction component (disclosed in Japanese Patent Application Laid-Open (kokai) No. 6-319945).
Concerning copper compounds, manganese compounds, etc. which serve as components of the aforementioned cleaning agents, those assuming the form of uniform microparticles and having a high BET specific surface area have heretofore been developed. Methods of producing copper oxide of such a type are known; for example, Japanese Patent Application Laid-Open (kokai) No. 2-145422 discloses a method of preparing copper oxide microparticles of such a type comprising adding a neutralizing agent formed of an ammonium salt to a high-purity copper nitrate solution, to thereby form microparticles; and washing, drying, and calcining the thus-formed microparticles. Methods of producing manganese dioxide of such a type include a method comprising mixing a dilute aqueous solution of potassium permanganate, a dilute aqueous solution of manganese sulfate, and concentrated sulfuric acid by stirring under heating so as to form precipitates, and washing and drying the precipitates, to thereby prepare manganese dioxide of large specific surface area. In recent years, through improvement in the shape of copper oxide, manganese oxide, etc. which serve as components of a cleaning agent in an attempt to obtain excellent characteristics as well as through development of compositions of the cleaning agent as described above, cleaning agents of more excellent cleaning power (i.e., performance in cleaning a harmful component per unit amount of cleaning agent) have been produced.
After the aforementioned cleaning agents containing copper oxide as a component thereof, those containing basic copper carbonate as a component thereof, those containing copper hydroxide as a component thereof, or those containing copper oxide and manganese oxide as components thereof have been used for cleaning a gas containing a phosphine or a silane gas, the cleaning agents are deactivated through immersion in water or through a similar method to a safe level where the human body and the environment are not adversely affected, and are subsequently treated as industrial wastes. If a copper component and a manganese component can be recovered from the industrial wastes and recycled as components of a cleaning agent for a harmful gas, not only effective use of resources but also protection of the environment could be attained.
However, nothing has been elucidated about the state of used cleaning agents which have sorbed a harmful component. In addition, studies have never been conducted on, for example, reactivity of a cleaning agent which has sorbed a harmful component or on possibility of generation of a harmful gas during dissolution in acid or neutralization of the cleaning agent. Thus, there has never been developed a method of recovering a copper component and/or a manganese component from a used cleaning agent and of restoring activity of the components so as to make them reusable.